Process of and electrolyte for refining copper



"tastes the. as, less ,ssi

PROCESS OF AND ELECTROLYTE FOR REFINING COPPER .lohn H. Schloen and Kurt Ekler, Montreal, Quebec, Canada, assignors to Canadian Copper Refiners Limited, Montreal East, Quebec, Canada, a corporation of Canada No Drawing. Application December 20, 1959, Serial No. 201,874

4 Claims.

Our present invention relates to a process of and an electrolyte composition for refining copper. More particularl", the present invention relates to an improvement in the present commercial process of electrolytically refining copper by the use of a novel combination of addition agents in the electrolyte, and particularly a novel addition agent, so as to obtain higher current efiiciencies than those attainable heretofore.

A conventional process of refining copper by electrolysis is to form the relatively impure copper into anodes; then suspend a plurality of such anodes in an electrolytic cell, in which there are cathodes alternately arranged with the anodes and preferably also provided at the ends of the alternately arranged anodes and cathodes. Each of the anodes in each cell is connected electrically in parallel and each of the cathodes in each cell is also electrically connected in parallel, so that the electric current supplied to the cell is simultaneously supplied to all the anodes from one electrical terminal and to all the cathodes from the opposite electrical terminal. In such known systems of refining copper, the electrolyte is circulated substantially continuously through the cell. Further details of a typical commercial installation to which the present invention has been applied will be given hereinafter.

If the electrolyte used in a system as aforesaid were solely an aqueous solution of sulphuric acid and copper sulphate, and with no addition agent or agents, it is found that the copper deposited upon the cathodes by the electrolytic action is not smoothly and uniformly deposited, but tends to form nodules and even trees, which branch out in the direction of the anodes and will eventually physically and electrically contact the anodes, causing a short circuit, thus lowering the current efficiency. This is a very real difiiculty because the normal distance between each anode and the adjacent cathodes is relatively small and may be about an inch. In order to oppose this nodule or tree formation and to obtain a cathode deposit which is reasonably smooth, dense and uniform, it has been. customary to use one or more addition agents in solution in the electrolyte. These addition agents have included many different types of materials, one of the most familiar and commonly used of which is glue. It has been found that when the concentration of glue is sufficient, a desirable type of cathode deposit can be obtained, 1. e., the deposit is reasonably uniform, it is dense and not noticeably crystalline in its appearance. It may, however, consist of very fine crystals. The glue appears to act, in part at least, to polarize the cathodes, but it does result in the substantial prevention of nodule or tree formation and results in a desired type of cathode deposit. As the concentration of glue is increased, however, even up to an amount which will give a desired type of cathode deposit, the voltage drop across the cell is increased; and as a result, the power cost is undesirably increase A principal object of the present invention is to provide an addition agent, which may be dissolved g in the electrolyte and which will serve to assist in the formation of desired cathode deposits, while giving a higher current efficiency than has been found possible using glue alone.

The present invention may thus be summarized as a process of refining copper commercially and an electrolyte composition for use in such coiumercial refining of copper, including not only some glue as was found desirable in accordance with certain prior art practices, but also an added material, which is available commercially under the trade name Avitone A. The particular description of this material, insofar as it is known, will be set forth more in detail hereinafter. is found that when this material is used alone (with no glue), the deposit of copper on the cathode is highly undesirable. On the other hand, when this material is used in conjunction with some glue, but not as much glue as would be required if no Avitone A were present, then the results from the point of view of cathode deposit are at least as good as and usually better than when glue alone is used. Also, the current eificiency is much greater than can be attained by the use of glue alone.

In practice, both the glue and the Avitone A" are first prepared as aqueous solutions and/or dispersions and are supplied preferably continuously to the electrolyte being circulated at the rate of about 0.6 to about 0.7 ounce of each (glue and Avitone A") per 1000 pounds of copper de-- posited on the cathodes. In practice, this amounts to establishing and maintaining a con centration of each of these materials in the electrolyte of about .45 to about .50 gram per liter.

Avitone A may be described as hydrolyzed, sulphonated derivatives of paraffinic hydrocarbons prepared in accordance with the process of Henke et 9.1., U. S. Patent No. 2,197,800, which accurately descri'besthe process or making Avitone A as follows:

reacting a, purified mixture of predominately aliphatic hydrocarbons having an initial boiling point by the A. S. T. M. method of at least 250 (3., and a dry point not greater than 360 C., a

J3 Saybolt viscosity of 32 to 52 seconds at 100 F., specific gravity of 0.7610 to 0.8200 at 15.5 C. and a refractive index of 1.4250 to 1.4500 at C., with a gaseous mixture of sulphur dioxide and chlorine, and hydrolyzing the resulting product.

No claim is made in the present application either to the structure of Avitone A as such, or to the process of making it, as both are recognized as no part of the present invention. The present application is directed and restricted to composition of an electrolyte including this material and to the process of commercially refining copper by electrolysis using an electrolyte including this material.

No other of the many materials tried during the research work by which the present invention was developed is considered to be the equivalent of Avitone A, for the reason that the re- 1 sults obtainable by other materials were not found to be comparable in the quality of the cathodes produced, or in current efiiciency, or ability to separate impurities, or several of these things, to the particular combination herein described and claimed. This material, Avitone A, is further desirable because of its relatively low price and the substantial economy which can be eiiected by its use, as well as by the superiority of the cathode deposits resulting from the use or" this material as herein taught.

In a typical commercial installation in which Avitone A has been successfully employed, there are 132 commercial cells, each of which is built of reinforced concrete cast in place and lined with antiinonial lead to resist the corrosive action of the sulphuric acid-copper sulphate electrolyte. The cells are suitably supported independently of the adjacent portions of the working floor and are suitably insulated from ground. Tank house electrolyte is circulated continuously at the rate of about 4.5 gallons per minute through each cell. Addition agents as herein taught are added dropwise and continuously to the circulating electrolyte. The temperature of the electrolyte, as delivered to each cell, is maintained at about 150 F. The copper anodes supplied to the cells contain various impurities, from the point of view of pure copper production, including silver, gold, selenium, tellurium and lead, which are insoluble; nickel and iron, which are soluble; and arsenic and antimony as well as some cuprous oxide, which are partly soluble. It is desired that these impurities be eliminated as far as possibleduring the elec trolysis and that a minimum thereof, particularly of the precious metals, be lost by inclusion, or occlusion, of the cathodes. impurities are soluble, it is necessary in order to maintain the efficiency of the electrolyte substantially continuously to keep drawing off electrolyte and replacing the withdrawn quantities with sulphuric acid and water. The copper content of the electrolyte is maintained uniform in a suitable manner, which per se forms no part of the present invention.

A typical analysis of the electrolyte being circulated in the system particularly described is as follows:

Aqueous solution, specific gravit 1.23 contain- Percent Copper 3.39 Free H2SO4 14.80 Chlorine .00065 Arsenic .069 Antimony .025 Iron .035 Nickel .588

In addition to this, the electrolyte in accordance with the present invention will have a concentration of glue of about .45 to about .50 gram per liter, and of Avitone A also of about .45 to about .50 gram per liter.

Since some of the In each of the cells in the installation being described there are 48 anodes arranged parallel to one another and spaced apart 4 inches on centers, and 49 cathodes arranged alternately with the anodes and parallel thereto.

It was found that when glue alone was used as the addition agent, a relatively higher concentration was required in order to get a desired type of cathode deposit. To obtain this result, it was found necessary to add glue at the rate of 18 ounces per day. Using glue aloneas the addition agent on a group of cells over an average test, the following data were obtained:

Voltage drop across a group of 18 During this test, glue was added at the rate of 12 ounces per day to the electrolyte used in the group of cells under test. The cathodes obtained from this test were satisfactory and represented average commercial production in accordance with prior art, which .is given in the present application as a control or standard of comparison. These cathodes were, however, rougher and not of as high a quality as those produced in accordance with the present invention.

Another similar test was made, usingno glue, but using the standard electrolyte to which a comparable amount of Avitone A was added as an addition agent. The cathodes obtained were totally unsatisfactory, appearing almost wholly granular and coarsely crystalline in their structure, so that when viewed in cross-section, the porous or crystalline portion of the deposit took up over of the thickness of the formed cathode and constituted substantially all the copper deposited, that is, leaving the original starting sheet cathode material placed in the cell at the beginning of the test as the only material of a desired dense and uniform nature. There were deep pits in the surface of the oathodes between thecrystals, in which electrolyte and impurities therefrom could be and was o'ccluded. The copper deposited in this test could, of course, have been remelted for subsequent use; but even under these circumstances, so much of the impurities was contained in the deposited material that the cathodes could be used only after substantial and expensive further refining. It was concluded, therefore, that Avitone A alone is totally unsatisfactory and is not a substitute for glue, which can be used in accordance with prior art teachings. No numerical data are reported from this test, due to the completely unsatisfactory character or the cathode deposit.

As contrasted with the use of either glue or Avitone A alone, the conjoint use of these two materials has been found to increase current efiiciency from about 91.9% available with glue as aforesaid, up to as much as 98%, which was the efficiency determined for one part of a test using both materials simultaneously. It was further found that the inclusion of precious metals in the cathode deposit was substantially reduced, and that the polarization of the electrodes was reduced, with a saving in electric power.

The data as to two tests using both glue and Avitone A simultaneously will now be given comparable to the data obtained from the test using glue alone, the figures hereinafter given in each case including a first figure representing a first test using both glue and Avitone A, and a second figure represents a second test respectively.

Voltage drop across 18 cells in series 4.10-4.31 volts. Amperes 17264-18788. Current density (amps./sq.ft.) 18.3-20.0 Time 24.38-22.18 days. Ampere-days 420896-416718. KiloWatt-days 17264797. Pounds of copper deposited 455183-448988. Current efficiency 95.8%94.4%.

In the second of these two tests, the final 1084 days of the test showed a current efficiency of 98.0%. It s noted that even though current densities are increased, the current efficiency is increased, which is contrary to what might normally be expected.

The concentration of both glue and Avitone A in the electrolyte in these two tests was was about .45 to about .50 gram per liter each. It appeared also that these addition agents were somehow used up in the process; and that the requirements for the supply of these addition agents for best results is generally proportional to the amount of copper deposited. Thus, by supplying an aqueous solution of each of these agents substantially continuously to the electrolyte being circulated in the 18 test cells used for the tests reported on above, it was found that about 12 ounces of glue and 12 ounces of "Avitone A each (dry weight) per day was required. Recalculated, this amount represents about 0.65 ounce of each (glue and of Avitone A) per 1000 lbs. of copper deposited. From other tests made using somewhat different proportions, it was found that the rate of supply, each of Avitone A and glue, should be from about 0.6 to 0.7 ounce per 1000 lbs. of copper deposited and that the concentration of each of these addition agents in the electrolyte should be about .45 to about .50 gram per liter.

No theory can be set forth definitely explaining the desirable results obtainable by the use of the present invention. It is found that the addition of Avitone A does not appear to increase the polarization or the voltage drop, as does the addition of glue in amounts greater than those desired in accordance with the present invention. On the other hand, the presence of Avitone A in the electrolyte enables 6 a small amount of glue to be used than would otherwise be required for best results. It is also found that the cathode deposits are hard, dense, and not noticeably crystalline. It was found that cathodes produced in accordance with the present invention included smaller amounts of precious metals, gold and silver, than cathodes made by previously known processes. No accumulation in the electrolyte or substances which might finally cause non-adherent or powdery deposits was noticed when following the present invention as aforesaid. Due to the absence of a coarsely crystalline cathode deposit, there is a lesser opportunity for suspended slimes to be occluded in the cathode deposit. Nodules and tree formation were substantially absent during operations according to the present invention.

The increase in current efficiency in the range where prior art current efiiciency was over is extremely difficult to obtain; so that the actual increase realized, namely from 91.9% to about 95.6% (average) represented a very appreciable improvement, which was unpredictable in View of the unsatisfactory results obtained by the use of Avitone A alone in electrolytic copper refining and certainly was not predictable from the other known uses for this material, which was principally as a textile fibre lubricant.

There is herein disclosed the composition of this novel addition material to the best of our present knowledge, and there also is disclosed the best known methods of use thereof and the composition of an electrolyte including this material. The appended claims are intended to include such equivalents of the present particular disclosure as will reasonably suggest themselves to those skilled in the art from the foregoing.

What is claimed is:

1. An electrolyte composition for use in the commercial electrolytic refining of copper, including an aqueous solution of H2304 and CuSOr, characterized in that said composition contains glue in a concentration of about .45 to .50 gram per liter and contains the hydrolyzed product of the reaction of a purified mixture of predominately aliphatic hydrocarbons having an initial boiling point by the A. S. T. M. method of at least 250 (3., and a dry point not greater than 360 C., a Saybolt viscosity of 32 to 52 seconds at F., specific gravity of 0.7610 to 0.8200 at 15.5 C. and a refractive index of 1.4250 to 1.4500 at 20 C.,

with a gaseous mixture of sulphur dioxide and chlorine, said hydrolyzed product being contained in said aqueous solution in a concentration of about .45 to about .50 gram per liter.

2. An electrolyte composition for use in the commercial electrolytic refining of copper, including an aqueous solution of H2804 and CuSO4, characterized in that said composition has mixed therewith an addition agent composition, the essential active ingredients of which consist of glue and the hydrolyzed product of the reaction of a purified mixture of predominately aliphatic hydrocarbons having an initial boiling point by the A. S. T. M. method of at least 250 C. and a dry point not greater than 360 0., a Saybolt viscosity of 32 to 52 seconds at 100 F., specific gravity of 0.7610 to 0.8200 at C. and a refractive index of 1.4250 to 1.4500 at 20 (3., with a gaseous mixture of sulphur dioxide and chlorine, said addition agent composition being added in such amounts that the electrolyte has a concentration of glue and of said hydrolyzed product each of about .45 to about .50 gram per liter.

'7 3. In the process of commercially refining. copper by electrolysis, using an electrolyte comprising an aqueous solution of sulphuric acid, the step of substantially continuously adding to the electrolyte an aqueous medium containing glue 5 and an aqueous medium containing the hydrolyzed product of the reaction of a purified mixture of predominately aliphatic hydrocarbons having an initial boiling point by the A. S. T. M. method of at least 250 C. and a dry point not greater than 360 0., a Saybolt viscosity of 3-2 to 52 seconds at 100 F., Specific gravity of 0.7610 to 0.8200 at 155 C. and a refractive index of 1.4250 to 1.4500 at 20 0., with a gaseous mixture of sulphur dioxide and chlorine, each at the rate of about 0.6 to about 0.7 ounce of glue and of said hydrolyzed product respectively per 1,000 pounds of copper deposited on the cathodes.

4. The process according to claim 3, wherein the rates of supply of said glue and said hydro" lyzed product are each about 0.65 ounce per 1,000

pounds of copper deposited on the cathodes.

JOHN H. SCHLOEN. KURT EKLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,544,726- Coloord. July '7, 1925 2,029,386 Pine Feb. 4, 1936 2,195,409 Flett Apr. 2, 1940 2,271,209 Schlotter Jan. 27, 1942 2,489,538 Phillips et a1 Nov. 29, 1949 OTHER REFERENCES Industrial and Engineering Chemistry, vol. 35, No. 1, January 1943, pp. 126-430. 

3. IN THE PROCESS OF COMMERCIALLY REFINING COPPER BY ELECTROLYSIS, USING AN ELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF SULPHURIC ACID, THE STEP OF SUBSTANTIALLY CONTINUOUSLY ADDING TO THE ELECTROLYTE AN AQUEOUS MEDIUM CONTAINING GLUE AND AN AQUEOUS MEDIUM CONTAINING THE HYDROLYZED PRODUCT OF THE REACTION OF A PURIFIED MIXTURE OF PREDOMINATELY ALIPHATIC HYDROCARBONS HAVING AN INITIAL BOILING POINT BY THE A.S.T.M. METHOD OF AT LEAST 250* C. AND A DRY POINT NOT GREATER THAN 360* C., A SAYBOLT VISCOSITY OF 32 TO 52 SECONDS AT 100* F., SPECIFIC GRAVITY OF 0.7610 TO 0.8200 AT 15.5* C. AND A REFRACTIVE INDEX OF 1.4250 TO 1.4500 AT 20* C., WITH A GASEOUS MIXTURE OF SULPHUR DIOXIDE AND CHLORINE, EACH AT THE RATE OF ABOUT 0.6 TO ABOUT 0.7 OUNCE OF GLUE AND OF SAID HYDROLYZED PRODUCT RESPECTIVELY PER 1,000 POUNDS OF COPPER DEPOSITED ON THE CATHODES. 